As it is generally known, digitized video data corresponding to a sequence of video scenes has a variable bit rate, since the amount of video data needed to generate each scene varies. For example, data rates for a video data stream originating from a broadcast quality source, such as from a DVD (Digital Versatile Disc) or similar source, vary from 10 Mbps or more down to a few 100 kbps, depending on the scene. However, when video data is transmitted across a communication network to a typical home, it passes through at least one relatively limited bandwidth channel. For example, when video data is passed over what is sometimes referred to as a “last mile” communication link to home equipment, a limited bandwidth channel is used. Such last mile technologies include satellite, coax cable or twisted pair, and typically are limited to between 3 and 4 Mbps of bandwidth. In existing systems, video data is sent over such links using a constant bit rate stream. The constant bit rate is selected such that data is not transferred faster than can be consumed by the real-time processing in the home equipment to generate the image. Such systems have limited capability to buffer video data that is transferred beyond what is immediately used in the receiving equipment to generate the display. Available video data exceeding the constant bit rate is accordingly not transferred. Accordingly, video data for a relatively complex scene cannot be fully transferred to the home equipment. Picture quality therefore suffers during scenes requiring relatively large amounts of video data, since the full set of video data is not available to the home equipment.
Moreover, because existing systems include minimal end system buffering, they operate by essentially transmitting video data in a continuous FIFO (First In First Out) manner, and retransmission of lost or damaged packets is not requested. This approach also prevents users from being able to fast forward through scenes as they watch the video, since there is no significant amount of video data available beyond that being used to generate the current scene.
For the above reasons, it would be desirable to have a new system for delivering digitized video information to an end user system that does not result in picture quality degradation for complex high data rate scenes. The new system should also enable retransmission of video frames in the case of an error, and allow a user to fast forward through video data beyond that for the current scene.